The architecture of standard computer systems or digital systems often include hardware components including central processing units, disk drives, input means, output means, and memories. All the hardware components are linked together by buses for data transfer and control purposes. Currently, a number of different specifications for bus are available for different system requirements and features.
Referring to FIG. 1 of the attached drawings, a computer system or a digital system that includes an ISA (Industry Standard Architecture) bus is shown. The computer system comprises a central processing unit 11, a memory 12, a PCI (Peripheral Component Interconnect) bridge 13, at least one PCI device 14, a PCI/ISA bridge 15, and a plurality of ISA devices D1 to Dn. The central processing unit 11 and the memory 12 are connected to a system bus 21 that is connected via the PCI bridge 13 to a PCI bus 22. The PCI bus 22 is a bus having specification formulated by PCISIG and serves to provide high speed data transfer in a microprocessor system. The PCI bus 22 is provided for connection with various PCI devices 14, such as interface devices including local area network interface card, video card, and input/output interface card. The PCI bus 22 is connected to an ISA bus 23 via the PCI/ISA bridge 15. The ISA bus 23 provides a connection with various ISA devices D1 to Dn. Each ISA device D1, D2, . . . , Dn, which is also referred to as a target device, operates to generate a device-end interrupt request signal D1_INT, D2_INT, . . . , Dn_INT, which is forwarded by the ISA bus 23 to an interrupt request signal controller 16 to carry out an interrupt service routine associated with the specific interrupt request signal.